In a semiconductor manufacturing process, conventionally, a silicon oxide film or the like is formed to have a desired pattern by performing plasma etching via a mask layer. With miniaturization of circuits in semiconductor devices, such plasma etching requires finer processes with high precision.
As one of techniques for performing such finer processes with high precision, there is a technique which uses a hard mask such as amorphous carbon or SOH (Spin On Hardmask) as a mask when contact holes are formed by plasma etching. It is known that a film containing carbon (C) of such amorphous carbon or SOH is etched by O2-based plasma and a mixture gas of CO and O2 is, for example, used as an etching gas (see, e.g., Japanese Patent Application Publication No. 2007-294943 and corresponding U.S. Patent Application Publication No. 2007-284335A).
However, as mentioned above, when the amorphous carbon is etched by plasma using the mixture gas of CO and O2 as the etching gas, for example, a diameter of a contact hole decreases due to miniaturization of an etching pattern, a so-called bowing effect that a shape of a side wall of the hole is curved outwardly is likely to occur. In addition, when a silicon oxide film is plasma-etched by using amorphous carbon or the like having bowing as a mask, there arises a problem that an error occurs in a shape of hole in the silicon oxide film. In addition, when a hole such as a contact hole or the like is formed, such bowing becomes noticeable as a diameter of the hole becomes smaller than 0.8 μm.